Thermal barrier coating ceramic layer thickness eddy current measurement method based on high-frequency resonance

Abstract

The invention discloses a thermal barrier coating ceramic layer thickness eddy current measuring method based on high-frequency resonance, and relates to the field of eddy current nondestructive testing. The thickness characteristics of the ceramic layer are decoupled through high-frequency excitation, the influence of the base body and the bonding layer on ceramic thickness measurement is restrained, and the thickness of the ceramic layer in the thermal barrier coating is obtained more accurately. Comprising the following steps: controlling the distribution of eddy current in a bonding layer and a substrate; equivalently expressing the coupling coefficient as an index relationship of the thickness of the ceramic layer; an RLC parallel resonance circuit is established, and an expression of delta Lab and the thickness of the ceramic layer is obtained; and obtaining a fitting coefficient in the expression of the delta Lab and the thickness of the ceramic layer by using the two samples, and obtaining a calibrated ceramic layer thickness characteristic curve. And an efficient solution is provided for the problem of accurate thickness measurement under multi-parameter coupling in the thermal barrier coating of the aero-engine.

Description

Technical Field

[0001] The present invention relates to the field of eddy current non-destructive testing, and particularly to an eddy current measurement method for the thickness of a ceramic layer of a thermal barrier coating based on high-frequency resonance. Background Art

[0002] A thermal barrier coating is a material protection technology applied to high-temperature working environments. It can reduce the working temperature of hot-end components, prevent components from suffering high-temperature corrosion, improve the combustion temperature and thermal efficiency of engines, reduce exhaust gas volume, thereby saving fuel and extending the life of blades. It is directly coated on a nickel-based superalloy substrate and usually consists of a ceramic thermal barrier layer and a metal bonding layer, as Figure 1 shown. Among them, the coating thickness and its uniformity are one of the key indicators of bonding manufacturing quality and service status, which are related to coating heat insulation performance, coating stress and bonding strength, life, coating material consumption and cost, etc. If the ceramic layer is too thin, its heat insulation performance will be reduced, increasing the risk of blade damage. If the ceramic layer is too thick, the huge difference in thermal expansion coefficients between the ceramic layer and the substrate will cause a significant increase in the interfacial stress of the coating, resulting in a weakening of the bonding strength between the ceramic layer and the substrate, and the coating is extremely likely to fall off. Therefore, the detection of ceramic layer uniformity is one of the important means for the quality control and in-service performance evaluation of thermal barrier coatings.

[0003] Currently, common methods for detecting the thickness of thermal barrier coatings include ultrasonic, infrared, microwave, terahertz, eddy current technology and other methods. Due to the 10% porosity in the ceramic layer of the thermal barrier coating, the microstructure is very uneven, often accompanied by pores and unmelted particles, which greatly affects other measurement methods except for the eddy current thickness detection method. Among them, the excitation of eddy current technology exists in the form of a "field", and the uneven microstructure of the ceramic layer does not affect the detection results of the thermal barrier coating. At the same time, eddy current technology has the characteristics of low cost, fast speed, small probe size, etc., and is very suitable for the evaluation of bonding manufacturing quality and service status.

[0004] The eddy current method based on electromagnetic induction has the advantages of low cost, high speed, high precision, etc., and is one of the ideal methods for non-destructive detection and evaluation of bonding thickness. Bonding has the characteristics of complex structure, thin thickness, low conductivity and small difference between the bonding layer and the substrate. Therefore, eddy current testing of thermal barrier coatings faces problems such as strong signal coupling, weak signal, and low resolution. In order to improve the thickness measurement resolution, many researchers have made improvements from the aspect of increasing the excitation frequency, but rely on high-frequency eddy currents to generate an inductive eddy current with sufficient density to increase the impedance signal strength. However, as the excitation frequency increases, signals are prone to introduce serious crosstalk between lines and external interference during transmission in coaxial cables, bringing complex environmental noise effects, and it poses a great challenge to obtain eddy current signals with high signal-to-noise ratio. Some scholars have also used the resonance method to improve the thickness detection resolution. When the reactance is zero, the system is in a resonant state, has the maximum response to the excitation signal of a specific frequency, realizes the directional selection and amplification function of the signal, thereby realizes signal enhancement, and applies this method to the detection of debonding defects in thermal barrier coatings. However, capturing the resonance frequency shift by the frequency sweep method is a relatively time-consuming method and it is difficult to meet the requirements of industrial rapid detection. In addition, due to the lack of a mathematical mapping relationship between the physical properties of the specimen to be tested and the impedance characteristics, these methods are mostly applied to defect detection, and there is still a blank in the thickness detection method based on high-frequency resonance. Summary of the Invention

[0005] In view of the above problems, the present invention proposes an eddy current measurement method for the thickness of the ceramic layer of a thermal barrier coating based on high-frequency resonance, which uses high-frequency excitation to decouple the thickness characteristics of the ceramic layer, suppresses the influence of the substrate and the bonding layer on the ceramic thickness measurement, and more accurately obtains the thickness of the ceramic layer in the thermal barrier coating.

[0006] The technical solution of the present invention is as follows: including the following steps:

[0007] Step 1, control the distribution of eddy currents in the bonding layer and the substrate;

[0008] Increase the excitation angular frequency ω, and use high-frequency excitation to make the eddy currents concentrate and penetrate in the bonding layer to eliminate the interference of the substrate;

[0009] Step 2, equivalently express the coupling coefficient K as an exponential relationship of the ceramic layer thickness;

[0010] First, according to the equivalent transformer model, derive the analytical expression of the change in the probe inductance ΔL and the mutual inductance index M in the transformer model, and simplify to obtain the analytical expression of ΔL and the coupling coefficient K, approximately eliminating the characteristic values containing the bonding layer thickness and conductivity; then, based on the Neumann formula and the Taylor series, equivalently express the coupling coefficient K as an exponential relationship of the ceramic layer thickness h t and obtain the fitting coefficient therein;

[0011] Step 3, establish an RLC parallel resonance circuit to obtain the change in the resonance inductance ΔLab Expression of the ceramic layer thickness;

[0012] A capacitor is connected in parallel at both ends of the coil to form an RLC parallel resonance circuit. The resonance frequency is obtained by sweeping the frequency. The excitation frequency is fixed at 1 / 2 of the peak value of the resonance inductance, and the change in resonance inductance ΔL output by the current system is used ab The change in coil inductance ΔL in the conventional transformer model is expressed exponentially, and ΔL is established ab Expression with the ceramic layer thickness, and the final fitting coefficient to be obtained is obtained;

[0013] Step 4: Fabricate an excitation, demodulation, and coil integrated probe, and perform digital signal and DC interaction with the detection instrument through the input and output ports at the top of the probe;

[0014] Step 5: Prepare two thermal barrier coating samples with different coating thicknesses, and use a high-frequency resonance eddy current detector to measure the change in resonance inductance ΔL at the point to be measured ab Characteristics, and obtain the true thickness of the point to be measured through a metallographic experiment;

[0015] Step 6: Use the two samples prepared in Step 5 to obtain the fitting coefficient in the expression of ΔL ab And the ceramic layer thickness;

[0016] Step 7: Use a high-frequency resonance eddy current detector to measure the sample to be measured, obtain its change in resonance inductance, and substitute it into the calibrated ceramic layer thickness characteristic curve to obtain the measured ceramic layer thickness of the sample.

[0017] Step 2 specifically includes:

[0018] Step 2.1: It can be deduced that the ΔL-M analytical expression is ΔL[1+(ΔR / ωΔL) 2 = L1K 2 , since the angular frequency ω is amplified in Step 1, the analytical expression of ΔL-M is simplified to the analytical expression of ΔL-K, that is, ΔL = L1K 2 , where K is the coupling coefficient, L1 is the self-inductance value of the coil, and ΔR and ΔL are the resistance change and inductance change of the coil on the specimen and in the air;

[0019] Step 2.2: Use the Neumann formula and Taylor series to equivalently express the coupling coefficient K as an exponential relationship with the ceramic layer thickness h t ΔL = aL1·exp(bh t ), where a and b are fitting coefficients.

[0020] Step 3 specifically includes:

[0021] Step 3.1. Connect capacitors at both ends of the coil to form an RLC parallel resonant circuit. Set the excitation frequency to half the peak value of the resonant inductance to amplify the inductance change through electromagnetic resonance.

[0022] Step 3.2: Establish the resonant inductance change ΔL ab The exponential fitting expression of the coil inductance change ΔL in the conventional transformer model is ΔL ab =c·exp(d·ΔL), where c and d are fitting coefficients;

[0023] Step 3.3: Combine the coupling coefficient K and the ceramic layer thickness approximate exponential expression in step 2 and the resonant inductance change ΔL in step 3.2 ab The exponential fitting expression of ΔL in the conventional transformer model is used to establish the resonant inductance change ΔL ab and the thickness of the ceramic layer h t The characteristic relationship ΔL ab =a1·exp(b1·h t ), where a1 and b1 are the final fitting coefficients to be determined.

[0024] Step 4 specifically includes:

[0025] Make an excitation module, demodulation module, and coil integrated probe, and interact with the detection instrument through the input and output ports on the top of the probe. The input port transmits the digital signal that controls the excitation module. After excitation, the coil is controlled. After that, the differential signal of the bridge is demodulated and output to the outside, and the output port transmits the demodulated amplitude and phase signal.

[0026] Step 6: Use the two calibration sample points in step 5 with known actual ceramic layer thickness and resonant inductance variation to calibrate the ceramic layer thickness characteristic curve established in step 3 to obtain ΔL. ab The fitting coefficients in the expression of the ceramic layer thickness include:

[0027] Assume that the thickness of the ceramic layer of the calibration piece 1 is h t1 , the change in resonant inductance is ΔL ab1 ; The thickness of the ceramic layer of calibration piece 2 is h t2 , the change in resonant inductance is ΔL ab2 , respectively into the characteristic curve expression ΔL of ceramic layer thickness detection ab =a1·exp(b1·h t ), we can get a1=exp[(h t2 lnΔL ab1 -h t1 lnΔL ab2 ) / (h t2 -h t1 )],b1=1 / (h t1-h t2 )·(lnΔL ab1 -lnΔL ab2 )。

[0028] The present invention solves the problems of impedance characteristic coupling of the ceramic layer, bonding layer and substrate in the detection of the ceramic layer by the traditional eddy current detection method, and the weak change of the eddy current characteristic signal and low detection sensitivity caused by the weak conductivity of the substrate. Combining the coupling characteristics of the ceramic layer, bonding layer and substrate in the thermal barrier coating, the law of eddy current attenuation is analyzed, and the high-frequency excitation is used to decouple the ceramic layer thickness characteristics and suppress the influence of the substrate and bonding layer on the ceramic thickness measurement. Aiming at the low conductivity of the bonding layer, the change amount of the impedance signal is increased by the inductance enhancement effect near the resonance point, a new resonant equivalent output inductance characteristic is established, and the mapping relationship between the new characteristic and the original impedance characteristic is constructed. Relying on the extremely high sensing ability of the new characteristic, the sensitivity of the characteristic signal is improved, and an integrated probe is designed to reduce the signal interference of the coaxial cable under high-frequency excitation.

[0029] Compared with the existing detection methods, the present invention has the following advantages:

[0030] First, using eddy current to detect the thickness of the ceramic layer of the thermal barrier coating can immune to the influence of the uneven microstructure of the ceramic layer. In addition, it also has the advantages of low cost, fast speed, small probe size, etc.

[0031] Second, by simplifying the analytical expression of ΔL-K through high-frequency eddy current, the influence of the conductivity and thickness change of the bonding layer and substrate on the detection result is weakened, and the accuracy of the ceramic layer thickness detection is improved.

[0032] Third, an approximate mapping relationship between the change amount of the resonant inductance ΔL ab at the near-resonant excitation position and the change amount of the coil inductance ΔL in the conventional transformer model is established, and this amplification relationship is used to improve the resolution of the ceramic layer thickness detection.

[0033] Fourth, an integrated probe of excitation, demodulation and coil is made. This probe can completely immune to the influence of the coaxial cable connection line on the detection result and improve the application ability of the device in a complex environment.

[0034] Therefore, the present invention provides an accurate, efficient and anti-interference technical solution for the detection of the ceramic layer thickness of the thermal barrier coating. According to the equivalent transformer model, the analytical expression of the change amount of the coil inductance ΔL and the equivalent coupling coefficient K is deduced, and the expression of ΔL-K is simplified by high-frequency eddy current, and the characteristic value containing the bonding layer thickness and conductivity is approximately eliminated; the resolution of the probe is improved by near-resonant frequency excitation, and the exponential expression relationship between ΔL ab and K is established, and through ΔL abExpress the thickness of the ceramic layer; fabricate an excitation, demodulation, and coil integrated probe to achieve data interaction between the probe and the device through digital and DC signals, and reduce the deformation noise generated by the coaxial cable.

[0035] Overall, the present invention improves the detection accuracy of the ceramic layer thickness, eliminates the influence of the bonding layer and the base on the ceramic layer thickness detection, and avoids the influence of the probe connection cable on the thickness detection result, greatly improving the application ability of the device in complex environments. Compared with the traditional eddy current detection technology, it has the characteristics of high sensitivity, strong anti-interference ability, and high on-site applicability, providing an efficient solution to the problem of accurate thickness measurement under multi-parameter coupling in the thermal barrier coating of aeroengines. Brief Description of the Drawings

[0036] Figure 1 : Schematic diagram of the eddy current ceramic layer thickness detection. L0 is the inductance of the coil, R0 is the resistance of the coil, K is the coupling coefficient, L b is the equivalent inductance of the eddy current in the specimen, R b is the equivalent resistance of the eddy current in the specimen, K is the coupling coefficient, C0 is the shunt capacitor, and there is a voltage source excitation between ab.

[0037] Figure 2 : Diagram of the exponential fitting degree between the change in resonant inductance and the change in probe inductance.

[0038] Figure 3 : Flowchart of the eddy current detection based on high-frequency resonance.

[0039] Figure 4 : Design diagram of the integrated probe structure. Detailed Description of the Invention

[0040] To clearly illustrate the technical features of this patent, the following will elaborate on this patent in detail through specific embodiments and in combination with its drawings.

[0041] The detection schematic diagram of the present invention is as shown in Figure 1 shown, and the flowchart of the eddy current measurement method for the ceramic layer thickness of the thermal barrier coating based on high-frequency resonance is as shown in Figure 3 shown, including the following steps:

[0042] Step 1, control the distribution of eddy currents in the bonding layer and the substrate;

[0043] Increase the excitation angular frequency ω. For example, increase the value of the excitation angular frequency ω to 30 MHz, and use high-frequency excitation to make the eddy currents concentrate and penetrate in the bonding layer to eliminate the interference of the substrate;

[0044] Step 2, equivalently express the coupling coefficient K as an exponential relationship with the ceramic layer thickness;

[0045] First, the analytical expression of the change in probe inductance ΔL and the mutual inductance index M in the transformer model is derived according to the equivalent transformer model, and the analytical expression of ΔL and the coupling coefficient K is obtained by simplification, approximately eliminating the eigenvalues containing the bond layer thickness and conductivity. Then, based on the Neumann formula and Taylor series, the coupling coefficient K is equivalently expressed as an exponential relationship with the ceramic layer thickness h t and the fitting coefficients therein are obtained;

[0046] Specifically:

[0047] Step 2.1, it can be derived that the ΔL-M analytical expression is ΔL[1+(ΔR / ωΔL) 2 =L1K 2 , since the angular frequency ω is amplified in Step 1, the analytical expression of ΔL-M is simplified to the analytical expression of ΔL-K, that is, ΔL=L1K 2 , where K is the coupling coefficient, L1 is the self-inductance value of the coil, and ΔR and ΔL are the resistance change and inductance change of the coil on the specimen and in the air; considering that the ceramic layer is non-conductive and ΔR is the measured value of the bond layer, after the value of the angular frequency ω is amplified, the influence of ΔR on the expression is greatly reduced, so the analytical expression can be simplified to achieve the purpose of eliminating the interference of the bond layer.

[0048] Step 2.2, the coupling coefficient K is equivalently expressed as an exponential relationship with the ceramic layer thickness h t by using the Neumann formula and Taylor series, ΔL=aL1·exp(bh t ), where a and b are fitting coefficients.

[0049] Step 3, an RLC parallel resonant circuit is established to obtain the expression of ΔL ab and the ceramic layer thickness;

[0050] In Step 3, especially considering that after the value of the angular frequency ω is amplified, the change in coil inductance ΔL will become smaller, which is not conducive to subsequent calculations. Therefore, in this case, an additional RLC parallel resonant circuit is added, and the change in resonant inductance ΔL ab is used to characterize the change in coil inductance ΔL to further accurately obtain the ceramic layer thickness;

[0051] A capacitor is connected in parallel at both ends of the coil to form an RLC parallel resonant circuit. The resonant frequency is obtained by sweeping the frequency. The excitation frequency is fixed at 1 / 2 of the peak value of the resonant inductance, and the change in resonant inductance ΔL ab output by the current system is used to exponentially express the change in coil inductance ΔL in the conventional transformer model. The fitting degree of its exponential relationship is as Figure 2 shown, to improve the resolution of this feature, an expression of ΔL ab and the ceramic layer thickness is established, and the final fitting coefficients to be obtained are obtained;

[0052] Specifically:

[0053] Step 3.1. Connect capacitors at both ends of the coil to form an RLC parallel resonant circuit. Set the excitation frequency to half the peak value of the resonant inductance to amplify the inductance change through electromagnetic resonance.

[0054] Step 3.2: Establish the resonant inductance change ΔL ab The exponential fitting expression of the coil inductance change ΔL in the conventional transformer model is ΔL ab =c·exp(d·ΔL), where c and d are fitting coefficients;

[0055] Step 3.3: Combine the coupling coefficient K and the ceramic layer thickness approximate exponential expression in step 2 and the resonant inductance change ΔL in step 3.2 ab The exponential fitting expression of the coil inductance change ΔL in the conventional transformer model is used to establish the resonant inductance change ΔL ab and the thickness of the ceramic layer h t The characteristic relationship ΔL ab =a1·exp(b1·h t ), where a1 and b1 are the final fitting coefficients to be determined.

[0056] Step 4: Make an integrated probe for excitation, demodulation, and coil, and interact digital signals and DC with the detection instrument through the input and output ports on the top of the probe;

[0057] Considering that after the numerical amplification of the angular frequency ω, the coaxial cable originally used for connection between the coil and the instrument (including the excitation module and demodulation module) will be regarded as a coil by the instrument, resulting in impedance changes when the coaxial cable deforms, affecting the detection accuracy. Therefore, the following optimizations were made in this case:

[0058] Step 4: Make an excitation module, a demodulation module, and a coil integrated probe. The input and output ports on the top of the probe are used to interact with the detection instrument. The input port transmits the digital signal that controls the excitation module. After excitation, the coil is controlled. After that, the differential signal of the bridge is demodulated and output to the outside. The output port transmits the demodulated amplitude and phase signal. The probe structure is as follows: Figure 4 As shown, the coaxial cable is eliminated and the deformation noise generated by the coaxial cable is reduced.

[0059] Step 5: Prepare two thermal barrier coating samples with different coating thicknesses and use a high-frequency resonant eddy current detector to measure the resonant inductance change ΔL at the test point. ab Features, and obtain the true thickness of the test point through metallographic experiments;

[0060] Step 6: Calculate ΔL using the two samples prepared in step 5 abThe fitting coefficient in the expression of the ceramic layer thickness;

[0061] Step 6: Use the two known calibration sample points of the true ceramic layer thickness and the change in resonant inductance in Step 5 to calibrate the ceramic layer thickness characteristic curve established in Step 3 to obtain ΔL. ab The fitting coefficient in the expression of the ceramic layer thickness; specifically:

[0062] Let the ceramic layer thickness of calibration piece 1 be h t1 , and the change in resonant inductance be ΔL ab1 ; Let the ceramic layer thickness of calibration piece 2 be h t2 , and the change in resonant inductance be ΔL ab2 , and substitute them into the characteristic curve expression of ceramic layer thickness detection ΔL ab = a1·exp(b1·h t ), to obtain a1 = exp[(h t2 lnΔL ab1 - h t1 lnΔL ab2 ) / (h t2 - h t1 ), and b1 = 1 / (h t1 - h t2 )·(lnΔL ab1 - lnΔL ab2 ).

[0063] Step 7: Use a high-frequency resonant eddy current detector to measure the sample to be tested, obtain the change in its resonant inductance, and substitute it into the calibrated ceramic layer thickness characteristic curve to obtain the measured ceramic layer thickness of the sample.

[0064] The present invention derives an analytic expression of the change in probe inductance ΔL and the equivalent coupling coefficient K based on the equivalent transformer model, simplifies the expression of ΔL - K through high-frequency eddy currents, and approximately eliminates the characteristic values containing the bond layer thickness and conductivity; improves the probe resolution by exciting at a near-resonant frequency, establishes an exponential expression relationship between ΔL ab , ΔL and K, and expresses the ceramic layer thickness through ΔL ab ; manufactures an integrated probe for excitation, demodulation, and coil, realizes data interaction between the probe and the device through digital signals and DC signals, and reduces the deformation noise generated by the coaxial cable. The present invention improves the detection accuracy of the ceramic layer thickness, avoids the influence of the probe connection cable on the thickness detection result, and greatly improves the application ability of the device in a complex environment.

[0065] There are many specific implementation ways of the present invention. The above description is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. An eddy current measurement method for the thickness of the ceramic layer of a thermal barrier coating based on high-frequency resonance, characterized in that, The following steps are involved: Step 1: Control the distribution of eddy current in the bonding layer and substrate; Increase the excitation angular frequency ω and use high-frequency excitation to concentrate the eddy current in the bonding layer, eliminating interference from the substrate; Step 2: Express the coupling coefficient K as an exponential relationship of the thickness of the ceramic layer; First, the analytical expression of the coil inductance change ΔL and the mutual inductance index M in the transformer model is derived based on the equivalent transformer model. The analytical expression of ΔL and the coupling coefficient K is simplified to approximately eliminate the eigenvalues containing the bonding layer thickness and conductivity. Then, based on the Neumann formula and Taylor series, the coupling coefficient K is equivalently expressed as an exponential relationship with the thickness h of the ceramic layer t and the fitting coefficient therein is obtained; Step 3: Establish an RLC parallel resonance circuit to obtain the change in resonance inductance ΔL ab and the expression for the ceramic layer thickness; A capacitor is connected in parallel across both ends of the coil to form an RLC parallel resonance circuit. The resonance frequency is obtained by frequency sweeping. The excitation frequency is fixed at 1 / 2 of the peak value of the resonance inductance, and the change in resonance inductance ΔL output by the current system is used. ab The change in coil inductance ΔL in the conventional transformer model is expressed exponentially, and ΔL is established. ab And the expression of the ceramic layer thickness, and the final fitting coefficient to be obtained is obtained. Step 4: Make an integrated probe for excitation, demodulation, and coil, and interact digital signals and DC with the detection instrument through the input and output ports on the top of the probe; Step 5: Prepare two thermal barrier coating samples with different coating thicknesses, and use a high-frequency resonant eddy current detector to measure the change in resonant inductance ΔL at the point to be measured ab characteristics, and obtain the true thickness of the point to be measured through a metallographic experiment; Step 6: Obtain ΔL by using the two samples prepared in Step 5 ab and the fitting coefficients in the expression of the ceramic layer thickness; Step 7: Use a high-frequency resonant eddy current detector to measure the sample to be tested, obtain its resonant inductance change, and bring it into the calibrated ceramic layer thickness characteristic curve to obtain the measured ceramic layer thickness of the sample.

2. The eddy current measurement method for the thickness of the ceramic layer of the thermal barrier coating based on high-frequency resonance according to claim 1, wherein Step 2 specifically includes: Step 2.1, it can be deduced that the analytical expression of ΔL-M is ΔL[1+(ΔR / ωΔL) 2 = L1K 2 , since the angular frequency ω is amplified in Step 1, the analytical expression of ΔL-M is simplified to the analytical expression of ΔL-K, that is, ΔL = L1K 2 , where K is the coupling coefficient, L1 is the self-inductance value of the coil, and ΔR and ΔL are the resistance change and inductance change of the coil on the specimen and in the air; Step 2.

2. Express the coupling coefficient K equivalently as an exponential relationship ΔL = aL1·exp(bh t ) of the ceramic layer thickness h t ), where a and b are fitting coefficients.

3. The eddy current measurement method for the thickness of the ceramic layer of the thermal barrier coating based on high-frequency resonance according to claim 1, wherein Step 3 specifically includes: Step 3.

1. Connect capacitors at both ends of the coil to form an RLC parallel resonant circuit. Set the excitation frequency to half the peak value of the resonant inductance to amplify the inductance change through electromagnetic resonance. Step 3.2: Establish the change in resonant inductance ΔL ab and the exponential fitting expression ΔL of the change in coil inductance ΔL in the conventional transformer model ab = c·exp(d·ΔL), where c and d are fitting coefficients; Step 3.

3. Combine the approximate exponential expression of the coupling coefficient K and the ceramic layer thickness in Step 2 and the change in resonant inductance ΔL in Step 3.2 ab with the exponential fitting expression of the change in coil inductance ΔL in the conventional transformer model to establish the characteristic relationship between the change in resonant inductance ΔL ab and the ceramic layer thickness h t as ΔL ab = a1·exp(b1·h t ), where a1 and b1 are the fitting coefficients to be finally determined.

4. A method for measuring the thickness of the ceramic layer of a thermal barrier coating based on high-frequency resonance eddy current according to claim 1, characterized in that Step 4 specifically includes: Make an excitation module, demodulation module, and coil integrated probe, and interact with the detection instrument through the input and output ports on the top of the probe. The input port transmits the digital signal that controls the excitation module. After excitation, the coil is controlled. After that, the differential signal of the bridge is demodulated and output to the outside, and the output port transmits the demodulated amplitude and phase signal.

5. A method for measuring the thickness of a thermal barrier coating ceramic layer based on high-frequency resonance eddy current according to claim 1, characterized in that Step 6 calibrates the ceramic layer thickness characteristic curve established in Step 3 by using the two calibration sample points of the known true ceramic layer thickness and the change in resonant inductance in Step 5 to obtain ΔL ab and the fitting coefficients in the expression of the ceramic layer thickness; specifically including: Let the thickness of the ceramic layer of the calibration piece 1 be h t1 , and the change in resonance inductance be ΔL ab1 ; the thickness of the ceramic layer of the calibration piece 2 be h t2 , and the change in resonance inductance be ΔL ab2 , and substitute them into the characteristic curve expression for ceramic layer thickness detection ΔL ab =a1·exp(b1·h t ), and we can get a1 = exp[(h t2 lnΔL ab1 -h t1 lnΔL ab2 ) / (h t2 -h t1 )], b1 = 1 / (h t1 -h t2 )·(lnΔL ab1 -lnΔL ab2 ).

Images